Recording module with a universal input for measurement of physical parameters

ABSTRACT

A recording card for the measurement of physical parameters includes at least one analogue-digital converter and at least one input connector for connection to a sensor. The recording card further includes a voltage source and a reference resistance arranged in series between the voltage source and a pin on the input connector. The analogue-digital converter has a reference input supplied with a voltage taken from the pins of the reference resistance and a conversion input supplied with a voltage taken from the pins of the input connector.

CROSS REFERENCE TO RELATED APPLICATION

The present application is the national stage under 35 U.S.C. 371 ofPCT/FR03/00516, filed Feb. 18, 2003.

BACKGROUND OF THE INVENTION

The present invention relates to an acquisition module for themeasurement of physical parameters, and relates in particular, but notlimitatively, to an autonomous acquisition card. Such an acquisitioncard comprises a connector to be connected to a sensor of physicalparameters such as for example temperature.

The acquisition card receives analogue data from the sensor, converts itinto digital data for a microcomputer or any other calculation andprocessing means.

DESCRIPTION OF THE RELATED ART

Generally, an acquisition card comprises several acquisition channels.Each acquisition channel comprises means for protection againstovervoltage and means for filtering and amplification of the analoguesignal. The acquisition channels inject the analogue signals into asingle multiplexer intended to connect a single acquisition channel toan analogue-to-digital converter at each instant.

The acquisition cards of the prior art comprise inputs which arepredetermined for a given physical parameter. For example an acquisitioncard designed to receive an input voltage cannot measure a current or aresistor without using specific adapters. These adapters are restrictingbecause they require a specific wiring and make it difficult to producea measurement.

Analogue-to-digital converters of Delta-Sigma type produced by AnalogueDevices® are known for example. The technical specifications of theseconverters mention a certain number of methods of implementation, inwhich for example two methods for measuring the temperature areidentified, using a platinum probe PT100 (temperature sensor) and usinga thermocouple, and a method for measuring the pressure using a pressuretransmitter. It is clearly noted that each method of implementationrequires a particular wiring and configuration.

SUMMARY OF THE INVENTION

The subject of the present invention is to remedy the above-mentioneddrawbacks by proposing an acquisition module capable of measuring alarge number of physical parameters, i.e. making the inputs of such anacquisition card quasi-universal, and principally for the parametersVoltage, Current and Resistance.

Another objective of the invention is limiting the use of an adaptorupstream of the inputs of an acquisition card, in particular the use ofconverters of external measurements.

The above-mentioned objectives are obtained with an acquisition moduleaccording to the invention, for the measurement of physical parameters,this module comprising at least one analogue-to-digital converter and atleast one input connector capable of receiving a sensor.

According to the invention, this acquisition module also comprises apower supply and a reference impedance arranged in series between thepower supply and a terminal of the input connector. Theanalogue-to-digital converter comprises a reference input supplied witha voltage taken at the terminals of the reference impedance and aconversion input supplied with a voltage taken via the input connectorat the sensor terminals. Moreover, this acquisition module comprisesmeans for delivering an image of the physical parameter measured by thesensor.

The present invention is characterized by the fact that advantageouslyit uses an analogue-to-digital converter which requires an externalreference. This converter can be of the type with differential inputsand by way of non-limitative example converters of the Delta-Sigma type,converters with successive approximations, flash converters or also rampconverters can be mentioned.

The analogue-to-digital converter can also be of the common mode inputtype; and it can comprises a first differential amplifier arrangedbetween the reference input and the reference impedance and a seconddifferential amplifier arranged between the conversion input and thesensor. In this case there is reason to define a common earth to thesetwo amplifiers.

For the most common measurements, generally, the power supply is avoltage and the impedance is a resistor. Once the characteristics of thevoltage source and the reference resistor are known, it is then possibleto deduce the value of the physical parameter measured from the digitalvalue generated by the analogue-to-digital converter. The same result isachieved by using a current source.

Advantageously, the acquisition module can comprise a memory for storingall of the parameters and variables.

In contrast to the cards of the prior art, the acquisition cardaccording to the invention can measure a voltage or a resistance withoutmodifying the architecture of the card and without interposing anyadapter.

Advantageously, each connecter comprises four pins so that many types ofassembly can be envisaged such as measurement on four wires using thefour pins or also measurement of voltage or current using only two pins.

With the process according to the invention independence from the powersupply and from the current passing through over the measurement branchis achieved.

As regards the measurement of current, the acquisition module alsocomprises a measurement resistor arranged at the terminals of the inputconnector. In this case, the measurement resistor has passing through itthe current to be measured and the current originating from the voltagesource. Measurement of the current simply requires the addition of ameasurement resistor. This additional resistor can be a resistorpreviously arranged on the card, its recognition being carried out byswitching of the input connector on this resistor in an automatic wayusing an analogue switch for example.

According to an advantageous characteristic of the invention, theacquisition module consists of a card which can be plugged into aprocessing unit such as a microcomputer. Consequently it can be equippedwith a PCI (Peripheral Component Interconnect) connector.

The power supply can be provided by the user or can come from anindependent source. This independent source can for example be themicrocomputer to which the acquisition module is connected via a USB(Universal Serial Bus) link for example.

Otherwise the power supply can be internal to the analogue-to-digitalconverter. It can also be programmable.

According to an embodiment of the invention, the acquisition module caninclude processing means capable of processing the digital dataoriginating from the analogue-to-digital converter in order to determinea value of the physical parameter measured. This characteristic would beadvantageous for an autonomous functioning in the case of an acquisitionmodule comprising integrated intelligence such as for example amicrocontroller associated with dedicated applications.

Moreover, means for protection against overvoltage can be arrangedbetween the analogue-to-digital converter on the one hand and thereference resistor and the connector on the other.

According to an embodiment of the invention, the acquisition module cancomprise a plurality of acquisition channels.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will also becomeapparent in the description below. In the attached drawings given by wayof non-limitative example:

FIG. 1 is a block diagram illustrating an analogue input channel of acard for acquisition of physical parameters according to the invention;

FIG. 2 is a simplified electronic diagram of an acquisition cardaccording to the invention for the measurement of a platinum probeaccording to the invention;

FIG. 3 is a simplified electronic diagram illustrating the basicprinciple for the measurement of current according to the invention;

FIG. 4 is a simplified electronic diagram illustrating the basicprinciple for the measurement of voltage according to the invention;

FIG. 5 reproduces the simplified electronic diagram of FIG. 1incorporating into it an operational amplifier; and

FIG. 6 is an electronic diagram illustrating an acquisition moduleaccording to the invention equipped with several acquisition channels onthe measurement branch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This acquisition card according to the invention comprises at least oneanalogue input channel represented by a connector equipped with twoterminals 3 and 4. The object of the measurement is intended to beconnected between the terminals 3 and 4. The acquisition card comprisesan analogue-to-digital converter 2 of Delta-Sigma type for which theconversion input is fed with the voltage at the terminals of theconnector (3, 4).

The reference input of the analogue-to-digital converter is suppliedwith a voltage V_(Ref) taken at the terminals of a resistor R. Theresistor R is arranged between a voltage source VS and the terminal 3 ofthe input connector, the terminal 4 of the input connector beingconnected directly to earth 5. The digital value at the output of theanalogue-to-digital converter 2 is directed to a processing unit 6 whichcan be a microcontroller arranged on the acquisition card or else themicroprocessor of a microcomputer into which the acquisition card isintegrated. Means for data storage 7, arranged on the acquisition card,store in the memory the characteristic values of the voltage source VSand of the resistor R in order to allow the processing unit to determinethe value of the physical parameter measured. By way of example, when atemperature sensor is arranged between terminals 3 and 4, the processingunit allows determination of the temperature of this sensor using thedigital value of the voltage measured at terminals 3 and 4.

In FIG. 2 an embodiment of the acquisition card according to theinvention for measuring a platinum probe of PT100 or PT1000 type or astrain gage, for example, is represented. Compared to the diagram ofFIG. 1, certain additional elements are incorporated. The protection andtesting means 8 which allow the inputs of the converter 2 to beprotected against any overvoltage should be noted. A current limitingresister 10 is arranged between the voltage source VS and the referenceresistor R. The input connector comprises four pins (or terminals) 3 a,3 b, 4 a, 4 b allowing measurements to be produced with maximumprecision according to the method with four wires. The fact of havingthese four pins permits many types of assembly.

The platinum probe 9 to be measured is directly connected to the inputconnector via four wires.

FIG. 3 illustrates another embodiment of the acquisition card 1according to the invention for measuring current.

For this, a new resistor 11 is added whose value is identical to thevalue of the reference resistor R. This resistor 11 is arranged at theterminals of the input connector. The current to be measured is thenapplied to the terminals of this resistor 11. The analogue voltage whichis then converted is the voltage at the terminals of this resistor 11.

The assembly of FIG. 3 can also serve for the measurement of any type ofthermocouple. The temperature compensation of the cold junction can thenbe produced with one of the available channels of the card, a softwareprogram compensating for and linearizing the measurements in theprocessing unit.

In FIG. 4 another embodiment of the acquisition card according to theinvention for measuring voltage is represented. The voltage to bemeasured is applied directly to the terminals of the input connector.

For the measurement of current and voltage (FIGS. 3 and 4), the supplyvoltage can be a reference voltage source internal to theanalogue-to-digital converter, this is a stabilized voltage which allowsoptimization of the measurements.

The invention is in particular characterized by the fact that thesuccessive measurements are obtained in a precise, reliable andconsistent way. For this, any drifts due to the power supply or to themeasuring current are guarded against. In fact, as regards themeasurement of the voltage or the platinum probe for example (resistivesensor), the current which passes through the measurement branch(I_(mes)) is the same as the one (I_(ref)) which passes through thereference resistor.

Moreover:

V_(ref)=R*I_(ref)——voltage present at the terminals of the referenceresistor and measured by the reference input of the analogue-to-digitalconverter. Similarly at the terminals of the resistor to be measured(the sensor):V _(mes) =R _(sensor) *I _(mes)It being understood that:I_(mes)=I_(ref)Consequently, as the converter produces at the output:S=K V _(mes) /V _(ref) ==>S=K*R _(sensor) /Ror S=K1 R_(sensor)The measurement is therefore not dependent on the supply voltage or onthe measurement current (K and K1 are two coefficients).

As is seen from all the embodiments represented, the acquisition cardaccording to the invention allows measurement of numerous physicalparameters without however greatly modifying the architecture. Only formeasurement of current, is a measurement resistor arranged at theterminals of the input connector.

FIG. 5 illustrates an embodiment in which the analogue-to-digitalconverter is no longer of the differential input type. In this case twoamplifiers 12 and 16 are arranged upstream of the reference andconversion inputs. A common earth 15 is then envisaged.

FIG. 6 illustrates a variant of the invention comprising severalacquisition channels, only two of the channels being represented. Twosensors 13 and 14 respectively arranged on the two input connectors areidentified. A reference voltage V_(ref) is retained and theanalogue-to-digital converter accepts two measurement voltages V_(in1′)and V_(in2′).

Of course the invention is not limited to the examples which have justbeen described and many variations can be made to these examples withoutexceeding the scope of the invention.

1. Acquisition module for the measurement of physical parameters,comprising: at least one analogue-to-digital converter, at least oneinput connector capable of receiving a sensor, a supply source and areference impedance arranged in series between said supply source and aterminal of the input connector, said analogue-to-digital convertercomprising differential inputs, a reference input supplied with avoltage taken at the terminals of said reference impedance and aconversion input supplied with a voltage taken via the input connectorat the sensor terminals, and means for delivering an image of thephysical parameter measured by the sensor.
 2. Acquisition moduleaccording to claim 1, characterized in that it comprises a memory forstoring parameters and variables.
 3. Acquisition module according toclaim 1, characterized in that it consists of a card which can beplugged into a processing unit such as a microcomputer.
 4. Acquisitionmodule according to claim 3, characterized in that the supply sourceoriginates from the processing unit.
 5. Acquisition module according toclaim 1, characterized in that the supply source is internal to theanalogue-to-digital converter.
 6. Acquisition module according to claim1, characterized in that the supply source is programmable. 7.Acquisition module according to claim 1, characterized in that itcomprises processing means capable of processing the digital dataoriginating from the analogue-to-digital converter in order to determinea value of the physical parameter measured.
 8. Acquisition moduleaccording to claim 1, characterized in that it comprises means forprotection against overvoltage arranged between the analogue-to-digitalconverter on the one hand and the reference resistor and the connectoron the other.
 9. Acquisition module according to claim 1, characterizedin that the analogue-to-digital converter consists of a Delta-Sigmaconverter.
 10. Acquisition module according to claim 1, characterized inthat the analogue-to-digital converter is of the common mode input typetogether with a first differential amplifier arranged between thereference input and the reference impedance and a second differentialamplifier arranged between the conversion input and the sensor. 11.Acquisition module according to claim 1, characterized in that itcomprises a plurality of acquisition channels.
 12. Acquisition modulefor the measurement of physical parameters, comprising: at least oneanalogue-to-digital converter; at least one input connector capable ofreceiving a sensor; a supply source and a reference impedance arrangedin series between said supply source and a terminal of the inputconnector; and image delivery part to deliver an image of the physicalparameter measured by the sensor, a reference resistor, saidanalogue-to-digital converter comprising differential inputs, areference input supplied with a reference voltage taken at the terminalsof said reference impedance, and a conversion input supplied with avoltage taken via the input connector at the sensor terminals, wherein,a first current which passes through measurement branch (“I_(mes)”) isthe same as a second current (“I_(ref)”) which passes through thereference resistor (“I_(mes)=I_(ref)”), a voltage present at theterminals of the reference resistor is measured by the reference inputof the analogue-to-digital converter and is equal to a resistance of theresistor times the second current (“V_(ref)=R*I_(ref)”), a voltage atthe terminals of the sensor is a resistance of the sensor times thefirst current (“V_(mes)=R_(sensor)*I_(mes)”), said converter produces anoutput measurement non-dependent on the supply voltage and non-dependenton measurement current.